Orphan nuclear receptors adopted by crystallography

Of the large nuclear hormone receptor superfamily of proteins, orphan nuclear receptors have remained a mystery owing to their lack of identified ligands and their constitutive nature. Now, structures of several ligand-binding domains of orphan receptors have provided some surprising insights that were not anticipated from molecular studies. Therefore, most orphan nuclear receptors have now been 'adopted' and their regulation has been shown to range from true ligand-independence to highly promiscuous ligand-dependence. Former orphan receptors have been found to contain ligand-binding pockets that range in volume from vast (>1600A3) to non-existent and have been shown to generate surface AF2 motifs that range from being multifunctionally active to distinctly inactive. Insights from these new structures illustrate how powerful a structural biology approach can be when integrated with molecular and cellular physiology.     

Identification of heteroarylenamines as a new class of antituberculosis lead molecules

Enamine-containing analogues of heteroarylquinones were prepared based on initial screening data observed against Mycobacterium tuberculosis H37Rv (Mtb). Several analogues showed moderate to good inhibitory activity, with one analogue (7) also demonstrating acceptable toxic selectivity (MIC 0.39 microg/mL, SI 15). Activity towards a range of single-drug-resistant strains of Mtb was suggestive of a novel mechanism of action for 7.     

Effect of short schemes on body composition measurements using Air-Displacement Plethysmography

Background

Air-displacement plethysmography (ADP) is becoming a popular method to assess body composition. Several studies have shown certain types of clothing can affect measurements of body density, however no study has specifically investigated the effect of cotton gym shorts and spandex bicycle shorts on body density.

Methods

Thirty-seven males (23.0 ± 3.2 yr., 177.3 ± 5.4 cm., 74.8 ± 7.5 kg.) and thirty-eight females (23.7 ± 5.3 yr., 163.6 ± 8.4 cm., 57.1 ± 7.0 kg.) had their body density measured by ADP in three clothing schemes: 1) a tight fitting Speedo^® swim suit (criterion measure), 2) cotton gym shorts, and 3) spandex bicycle shorts. The clothing was provided by the University of Oklahoma Body Composition Laboratory and the testing schemes were performed in random order.

Results

The regression of body density by the criterion measure against body density while wearing cotton gym shorts for the entire group (y = 0.001 + 0.991x, SEE = 0.003 g/cm³) and the females (y = 0.059 + 0.934x, SEE = 0.003 g/cm³) did not significantly deviate from the line of identity. However in males the regression significantly deviated from the line of identity (y = 0.052 + 0.944x, SEE = 0.002 g/cm³). Body density by the criterion measure and body density while wearing spandex bicycle shorts did not significantly differ from the line of identity for the entire group (y = -0.018 + 1.013x SEE = 0.003 g/cm³), in males (y = -0.002 + 1.001x, SEE = 0.003 g/cm³), or females (y = 0.073 + 0.925x, SEE = 0.003 g/cm³). Residual plot analysis revealed no group or gender bias in either the cotton gym shorts or in the spandex bicycle shorts.

Conclusion

It would appear bicycle spandex shorts are an acceptable alternative to a Speedo^® like swim suit, however we advise that subjects adhere to the strict clothing protocol that is recommended by the manufacturer.

     

Receptor for retrograde transport in the apicomplexan parasite Toxoplasma gondii

Toxoplasma gondii and its apicomplexan relatives (such as Plasmodium falciparum, which causes malaria) are obligate intracellular parasites that rely on sequential protein release from specialized secretory organelles for invasion and multiplication within host cells. Because of the importance of these unusual membrane trafficking pathways for drug development and comparative cell biology, characterizing them is essential. In particular, it is unclear what role retrieval mechanisms play in parasite membrane trafficking or where they operate. Previously, we showed that T. gondii's beta-COP (TgBetaCOP; a subunit of coatomer protein complex I, COPI) and retrieval reporters localize exclusively to the zone between the parasite endoplasmic reticulum (ER) and Golgi apparatus. This suggested the existence of an HDEL receptor in T. gondii. We have now identified, cloned, and sequenced this receptor, TgERD2. TgERD2 localizes in a Golgi or ER pattern suggestive of the HDEL retrieval reporter (K. M. Hager, B. Striepen, L. G. Tilney, and D. S. Roos, J. Cell Sci. 112:2631-2638, 1999). A functional assay reveals that TgERD2 is able to complement the Saccharomyces cerevisiae ERD2 null mutant. Retrieval studies reveal that stable expression of a fluorescent exogenous retrieval ligand results in a dispersal of betaCOP signal throughout the cytoplasm and, surprisingly, results in betaCOP staining of the vacuolar space of the parasite. In contrast, stable expression of TgERD2GFP does not appear to disturb betaCOP staining. In addition to TgERD2, Toxoplasma contains two more divergent ERD2 relatives. Phylogenetic analysis reveals that these proteins belong to a previously unrecognized ERD2 subfamily common to plants and alveolate organisms and as such could represent mediators of parasite-specific retrieval functions. No evidence of class 2 ERD2 proteins was found in metazoan organisms or fungi.     

Restructuring and Health in Canadian Coastal Communities

Environmental and socioeconomic restructuring has had profound consequences for coastal communities in Canada. The decline of traditional resource-based industries—fisheries, forestry, and mining—and the emergence of new economic activities, such as tourism and aquaculture, compounded by concurrent shifts in social programs, have affected the health of environments, communities, and people. Drawing on research conducted as part of the interdisciplinary major collaborative research initiative Coasts Under Stress, we examined the implications of interactive restructuring for the health of people and communities on Canada’s east and west coasts. The research is guided by a socioecological framework that identifies the pathways from interactive restructuring through health determinants to health risks and health outcomes. The utility of the proposed framework is exemplified by a specific place-based example in Prince Rupert, British Columbia, and a case-based example from coastal communities in Newfoundland and Labrador. A focus on interactive restructuring draws our attention to the many challenges associated with promoting health in a context of rapid and often accelerating environmental and institutional change that is relevant to other areas and contexts.     

Methionine oxidation and aging

It is well established that many amino acid residues of proteins are susceptible to oxidation by various forms of reactive oxygen species (ROS), and that oxidatively modified proteins accumulate during aging, oxidative stress, and in a number of age-related diseases. Methionine residues and cysteine residues of proteins are particularly sensitive to oxidation by ROS. However, unlike oxidation of other amino acid residues, the oxidation of these sulfur amino acids is reversible. Oxidation of methionine residues leads to the formation of both R- and S-stereoisomers of methionine sulfoxide (MetO) and most cells contain stereospecific methionine sulfoxide reductases (Msr's) that catalyze the thioredoxin-dependent reduction of MetO residues back to methionine residues. We summarize here results of studies, by many workers, showing that the MetO content of proteins increases with age in a number of different aging models, including replicative senescence and erythrocyte aging, but not in mouse tissues during aging. The change in levels of MetO may reflect alterations in any one or more of many different mechanisms, including (i) an increase in the rate of ROS generation; (ii) a decrease in the antioxidant capacity; (iii) a decrease in proteolytic activities that preferentially degrade oxidized proteins; or (iv) a decrease in the ability to convert MetO residues back to Met residues, due either to a direct loss of Msr enzyme levels or indirectly to a loss in the availability of the reducing equivalents (thioredoxin, thioredoxin reductase, NADPH generation) involved. The importance of Msr activity is highlighted by the fact that aging is associated with a loss of Msr activities in a number of animal tissues, and mutations in mice leading to a decrease in the Msr levels lead to a decrease in the maximum life span, whereas overexpression of Msr leads to a dramatic increase in the maximum life span.     

Viral delivery of an epitope from Haemophilus influenzae induces central nervous system autoimmune disease by molecular mimicry

Multiple sclerosis (MS) is an autoimmune CNS demyelinating disease in which infection may be an important initiating factor. Pathogen-induced cross-activation of autoimmune T cells may occur by molecular mimicry. Infection with wild-type Theiler's murine encephalomyelitis virus induces a late-onset, progressive T cell-mediated demyelinating disease, similar to MS. To determine the potential of virus-induced autoimmunity by molecular mimicry, a nonpathogenic neurotropic Theiler's murine encephalomyelitis virus variant was engineered to encode a mimic peptide from protease IV of Haemophilus influenzae (HI), sharing 6 of 13 aa with the dominant encephalitogenic proteolipid protein (PLP) epitope PLP(139-151). Infection of SJL mice with the HI mimic-expressing virus induced a rapid-onset, nonprogressive paralytic disease characterized by potent activation of self-reactive PLP(139-151)-specific CD4(+) Th1 responses. In contrast, mice immunized with the HI mimic-peptide in CFA did not develop disease, associated with the failure to induce activation of PLP(139-151)-specific CD4(+) Th1 cells. However, preinfection with the mimic-expressing virus before mimic-peptide immunization led to severe disease. Therefore, infection with a mimic-expressing virus directly initiates organ-specific T cell-mediated autoimmunity, suggesting that pathogen-delivered innate immune signals may play a crucial role in triggering differentiation of pathogenic self-reactive responses. These results have important implications for explaining the pathogenesis of MS and other autoimmune diseases.     

The CD200 receptor is a novel and potent regulator of murine and human mast cell function

CD200R is a member of the Ig supergene family that is primarily expressed on myeloid cells. Recent in vivo studies have suggested that CD200R is an inhibitory receptor capable of regulating the activation threshold of inflammatory immune responses. Here we provide definitive evidence that CD200R is expressed on mouse and human mast cells and that engagement of CD200R by agonist Abs or ligand results in a potent inhibition of mast cell degranulation and cytokine secretion responses. CD200R-mediated inhibition of FcepsilonRI activation was observed both in vitro and in vivo and did not require the coligation of CD200R to FcepsilonRI. Unlike the majority of myeloid inhibitory receptors, CD200R does not contain a phosphatase recruiting inhibitory motif (ITIM); therefore, we conclude that CD200R represents a novel and potent inhibitory receptor that can be targeted in vivo to regulate mast cell-dependent pathologies.     

Sequential immune escape and shifting of T cell responses in a long-term survivor of melanoma

Immune-mediated control of tumors may occur, in part, through lysis of malignant cells by CD8(+) T cells that recognize specific Ag-HLA class I complexes. However, tumor cell populations may escape T cell responses by immune editing, by preventing formation of those Ag-HLA complexes. It remains unclear whether the human immune system can respond to immune editing and recognize newly arising escape variants. We report an example of shifting immune responses to escape variants in a patient with sequential metastases of melanoma and long-term survival after surgery alone. Tumor cells in the first metastasis escaped immune recognition via selective loss of an HLA haplotype (HLA-A11, -B44, and -Cw17), but maintained expression of HLA-A2. In the second metastasis, immune escape from an immunodominant MART-1-specific T cell response was mediated by HLA class I down-regulation, resulting in a failure to present this epitope, but persistent presentation of a tyrosinase-derived epitope. Consequent to this modification in tumor Ag presentation, the dominant CTL response shifted principally toward a tyrosinase-targeted response, even though tyrosinase-specific CTL had been undetectable during the initial metastatic event. Thus, in response to immune editing of tumor cells, a patient's spontaneous T cell response adapted, gaining the ability to recognize and to lyse "edited" tumor targets. The observation of both immune editing and immune adaptation in a patient with long-term survival after surgery alone demonstrates an example of immune system reactivity to counteract the escape mechanism(s) developed by tumor cells, which may contribute to the clinical outcome of malignant disease.     

Solution structure of a CCHHC domain of neural zinc finger factor-1 and its implications for DNA binding

The structure of a CCHHC zinc-binding domain from neural zinc finger factor-1 (NZF-1) has been determined in solution though the use of NMR methods. This domain is a member of a family of domains that have the Cys-X(4)-Cys-X(4)-His-X(7)-His-X(5)-Cys consensus sequence. The structure determination reveals a novel fold based around a zinc(II) ion coordinated to three Cys residues and the second of the two conserved His residues. The other His residue is stacked between the metal-coordinated His residue and a relatively conserved aromatic residue. Analysis of His to Gln sequence variants reveals that both His residues are required for the formation of a well-defined structure, but neither is required for high-affinity metal binding at a tetrahedral site. The structure suggests that a two-domain protein fragment and a double-stranded DNA binding site may interact with a common two-fold axis relating the two domains and the two half-sites of the DNA-inverted repeat.